Smoke that drifted from the Tesoro refinery near Martinez today was caused by problems with the refinery's primary steam generation unit, a Tesoro spokeswoman said.

The problem with the unit was reported at 11:47 a.m. and resulted in excessive flaring with visible smoke coming from the refinery at 150 Solano Way, Tesoro spokeswoman Patty Deutsche said.

The smoke prompted Contra Costa Health Services officials to issue a health advisory for the surrounding areas of Martinez, Pacheco, North Concord and Clyde, warning that people, primarily those with pre-existing medical conditions, could experience respiratory problems.

The smoke eventually dissipated and the alert was lifted as of 1:50 p.m., county hazardous materials specialist Maria Duazo said. No injuries were reported.

The steam generation unit has since resumed operating and the refinery is no longer flaring, Deutsche said. Deutsche said Tesoro is working with county health officials and other regulatory agencies investigating the incident.

"Our main priority is to safely return the refinery to normal operations and to minimize the impact to the community and the environment," she said.

The refinery has a crude oil capacity of 166,000 barrels per day and produces motor fuels, as well as heavy fuel oils, liquefied petroleum gas and petroleum coke, according to its website.